add delete confirmation to task on paper manage page

— RW + DT
You're already stubbing out the delete route for the card in this test.  You might as well assert that you posted to it here.  `ok(_.findWhere(server.requests....` you can find examples of it in some other integration tests we've written.  At that point if you have a controller spec that makes sure the `TasksController#destroy` action works then you've made the portion of the capybara spec that's testing deletion obsolete.  I wanna make sure you guys aren't just including extra full-stack tests just for the heck of it.  You've already done the hard part and written a good ember test; you might as well take full advantage of it.